PROJECT SUMMARY Despite substantially declining during the past 2 decades, teenage pregnancy rates remain the highest in the United States compared to other Western countries. Being born to a teenage mother has been noted in the literature and public perceptions for many decades as a permanent source of developmental disadvantages for children. Although a strong body of literature has compared children of teen mothers to children of older mothers, less known are factors contributing to variations in developmental outcomes among children of teen mothers. As such, the relevant knowledge base is limited in informing prevention programming for healthy development among children of teen mothers. Capitalizing on unique longitudinal studies of teen mothers and their children, the proposed study aims to remedy these gaps with an explicit focus on and in-depth investigation of maternal history of substance use and exposure to adverse childhood experiences (ACEs) as two key factors promoting within-group variability in children of teen mothers. Specifically, first, we will investigate whether the timing and longitudinal trajectories of teen mothers? substance use beyond the prenatal period affect child developmental outcomes. Second, we will examine whether maternal ACEs, which are intergenerational risk factors preceding the child?s birth, influence child development and intersect with a more proximal maternal risk factor, maternal substance use. The proposed study will leverage access to existing two-cohort Young Women and Child Development Study (YCDS) panels. Cohort 1 (C1, n = 240) spans 17 years of both the mothers? and child?s life course. At the last wave of cohort 1data collection, children were 17 years old and mothers were 33.8 years old on average. Cohort 2 (C2, n = 255) encompasses 14 years of both mothers? and child?s life course. At the last wave of cohort 2 data collection, children were 13.5 years old and mothers were 30.3 years old on average. This rich dataset has all the key elements to achieve the aims of the proposed study, including (a) prospective and repeated assessment of child development from infancy through adolescence in both cohorts using validated assessment packages spanning child executive functioning, language development, externalizing behaviors, and other developmental measures; (b) annual or semiannual assessments of maternal substance use from pregnancy to 17 years postpartum in C1 and 13.5 years postpartum in C2; and (c) assessment of maternal ACEs. The comprehensiveness of the datasets, with 14 to 17 waves of annual assessment, offers a novel opportunity to use longitudinal modeling strategies to identify the developmental timing and dynamic changes in maternal substance use among pregnant women, link them to child developmental outcomes, and then link those back to maternal ACEs exposure. The proposed study will maximize the use of data from both cohorts by adopting a cross-validation strategy and an integrated strategy of combining data with tests of cohort effect.